MMM V3 Dead Short on Lipo!

[jhautz]

Originally Posted by pasan

Which is what he should've done after the very first spark.

Hind sight being 20/20, I agree. Easy to loose you head in the heat of the moment when the panic and frustration set in. LOL

I did throw a multi meter on it after the 2nd spark, and before the repeated sparking with the 6 cell NiMH pack, but got a really wierd reading. I couldnt get it to give me a consistent measurement. It started off with a very low resistance reading at almost infinity and then over a few seconds kept going up and up to a very high number. It was strange. I also measured the resistance between the plugs on the working V2 I pulled out of the truggy and got some "dancing" numbers. Not sure why that would be, but that little test basically didnt tell me anything. so I went back to the "brute force" testing . lol

[BrianG]

Originally Posted by jhautz

Hind sight being 20/20, I agree. Easy to loose you head in the heat of the moment when the panic and frustration set in. LOL

I did throw a multi meter on it after the 2nd spark, and before the repeated sparking with the 6 cell NiMH pack, but got a really wierd reading. I couldnt get it to give me a consistent measurement. It started off with a very low resistance reading at almost infinity and then over a few seconds kept going up and up to a very high number. It was strange. I also measured the resistance between the plugs on the working V2 I pulled out of the truggy and got some "dancing" numbers. Not sure why that would be, but that little test basically didnt tell me anything. so I went back to the "brute force" testing . lol

What you saw was a capacitor charging up. In resistance-measuring mode, meters output a small voltage through a precision resistor and measure the resulting small current (actually it looks at the voltage drop across the internal precision resistor), and then use that to calculate the component resistance being measured. At first, they have ~0v (which would look like ~0 resistance to a meter). As the cap(s) charge, the difference in voltage is less, which reduces the current in the meter's resistor, which appears as higher resistance. At some point, the meter will read infinite resistance because there is no current flow. Actually, you could use this to calculate the meter's output resistance, but that's another story. Anyway, this is why measuring resistance is sometimes useless while the component is in a circuit.

The fact that you did see the resistance change tells me that there is no short circuit. But that still doesn't explain the "huge" spark.

[SpEEdyBL]

If the capacitors are at 0 volts, and you plug in a 5s pack, YOU WILL see a decent spark. That's normal, but usually the second time you try to plug it in there is no spark. Maybe there is just low enough resistance so that the capacitor drains rather quickly on its own and will always cause a spark every time you plug a pack in. Or maybe castle just decided to use mega capacitors on the V3s. Lol

[jhautz]

No... It wasnt a normal spark. Trust me Ive plugged in more than my share of these things in my day. lol It was huge crack like when you accidnetally short a lipo. It melted the ends of the deans plug. It was like an arc welder not capacitor spark.



The fact that it works now is the thing thats totally freaky to me.

[glassdoctor]

Originally Posted by jhautz

so like an idiot.... I tried plugging it in again. WHAP!!! another HUGE spark. Scared the poop out of me again even though I was mostly expecting it.

Somehow that was one of the funniest things I've read in a while... sorry man!!!

So this MMM is still working now???

[jhautz]

Originally Posted by glassdoctor

So this MMM is still working now???

Yep. Ran it again yesterday. 2 and a half more full packs through it and its still running.